Photodiode array, method for manufacturing photodiode array, epitaxial wafer, and method for manufacturing epitaxial wafer

ABSTRACT

Provided are a photodiode array and its manufacturing method, which maintain the crystalline quality of an absorption layer formed on a group III-V semiconductor substrate to obtain excellent characteristics, and which improve the crystallinity at the surface of a window layer; an epitaxial wafer used for manufacturing the photodiode array; and a method for manufacturing the epitaxial wafer. A method for manufacturing a photodiode array  1  having a plurality of absorption regions  21 , includes the steps of: growing an absorption layer  7  on an n-type InP substrate  3 ; growing an InP window layer on the absorption layer  7 ; and diffusing a p-type impurity in regions, in the window layer  11 , corresponding to the plurality of absorption regions  21 . The window layer  11  is grown by MOVPE using only metal-organic sources, at a growth temperature equal to or lower than that of the absorption layer  7.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photodiode arrays and epitaxial wafers,which use compound semiconductors, and manufacturing methods thereof.More particularly, the invention relates to photodiode arrays andepitaxial wafers, which use InGaAs/GaAsSb type-II semiconductors, andmanufacturing methods thereof.

2. Description of the Background Arts

Recently, much research and development for group III-V compoundsemiconductors using an InP substrate has been promoted because the bandgap energies of these compound semiconductors correspond to the nearinfrared region. Non-Patent Document 1 (R. Sidhu, “Long-wavelengthPhotodiode on InP Using Lattice-Matched GaInAs—GaAsSb Type-II QuantumWells”, IEEE Photonics Technology Letters, The Institute of Electricaland Electronics Engineers, Volume 17, No. 12, pp. 2715-2717, (2005))reports a photodiode having a cutoff wavelength of 2.39 μm, in which anabsorption layer having an InGaAs—GaAsSb type-II multiple quantum wellstructure is formed on an InP substrate, and a pn junction is formed bya p-type or n-type epitaxial layer. Further, Non-Patent Document 1proposes a photodiode having a cutoff wavelength of 2 μm to 5 μm, whichuses an InGaAs—GaAsSb strain-compensated multiple quantum well structurein order to obtain such a longer cutoff wavelength.

Non-Patent Document 2 (M. Peter, “Light-emitting diodes and laser diodesbased on a Ga_(1-x)In_(x)As/GaAs_(1-y)Sb_(y) type II superlattice on InPsubstrate”, APPLIED PHYSICS LETTERS, American Institute of Physics,Volume 74, No. 14, pp. 1951-1953, (1999)) discloses light-emittingdiodes (LEDs) each including an absorption layer having an InGaAs—GaAsSbtype-II multiple quantum well structure, and an InP cladding layer grownon the absorption layer. The InP cladding layer in the LED is grown at640° C., using phosphine (PH₃) as a raw material for P.

Non-Patent Document 3 (D. Keiper, “Metalorganic vapour-phase epitaxy(MOVPE) growth of InP and InGaAs using tertiarybutylarsine (TBA) andtertiarybutylphosphine (TBP) in N2 ambient”, Journal of Crystal Growth,ELSEVIER, 204, pp. 256-262, (1999)) discloses growth of InGaAs andInGaAs/InP by metal-organic vapor phase epitaxy (MOVPE) usingtertiarybutylarsine (TBAs), tertiarybutylphosphine (TBP),trimethylgallium (TMGa), and trimethylindium (TMIn), and investigationon growth condition dependence of surface defects during the growth. InNon-Patent Document 3, an epitaxial wafer having a low density ofsurface defects is obtained at a relatively high growth temperature of660° C. or more.

Patent Document 1 (Japanese Laid-Open Patent Publication No.2001-144278) discloses a photodiode array having a mesa structure inwhich photodiodes each composed of laminated semiconductor layers areisolated from each other by etching. This photodiode array ismanufactured as follows. An n-type InP layer, an undoped InGaAs lightabsorption layer, and a p-type InP window layer are disposed in thisorder on an n-type InP substrate. The InGaAs light absorption layer andthe p-type InP window layer are subjected to etching to form individualphotodiodes isolated from each other, and the photodiodes are coatedwith an insulating film. Then, a p-type ohmic electrode is formed on thep-type InP window layer of each photodiode while a common n-type ohmicelectrode is formed on the rear surface of the n-type InP substrate.

SUMMARY OF THE INVENTION

In the photodiode array disclosed in Patent Document 1, it is desired toreduce the percentage of defectives among a plurality of photodiodes(hereinafter, also referred to as pixels) arranged one-dimensionally ortwo-dimensionally. Since defective pixels are caused by irregularities(surface defects) having a height of 10 nm or more at the surface of thewindow layer, it is important to reduce the density of surface defects.

Generally, in manufacturing of the photodiode array having the structuredisclosed in Patent Document 1, phosphine (PH₃) is used as a rawmaterial for P when an InP window layer is formed on an InGaAs lightabsorption layer. In this case, the growth temperature must be set at ahigh temperature of 640° C. as described in Non-Patent Document 2.Therefore, the crystalline quality of the light absorption layer isdegraded by heat when the InP window layer is grown, which contributesto pixel defects.

In Non-Patent Document 1, an InGaAs layer is provided as a window layeron the absorption layer. However, when an electrode and a passivationlayer are formed on the InGaAs layer, dark current at the crystalsurface is undesirably increased because of insufficient accumulation oftechnical knowledge.

Non-Patent Document 3 describes that surface defects of InP aresignificantly reduced by setting the InP growth temperature at 660° C.or more. However, if the InP window layer is grown at such a hightemperature as 660° C. or more, the crystalline quality of theabsorption layer is degraded by heat when the InP window layer is grown,which contributes to pixel defects.

Accordingly, it is an object of the present invention to provide: aphotodiode array and its manufacturing method, which can improve thecrystalline quality of an absorption layer formed on a group III-Vsemiconductor substrate to realize excellent characteristics, and whichcan improve the crystallinity at the surface of a window layer; anepitaxial wafer used for manufacturing of the photodiode array; and amethod for manufacturing the epitaxial wafer.

In order to solve the above-described problems, the present inventionprovides a method for manufacturing a photodiode array having aplurality of absorption regions that are one-dimensionally ortwo-dimensionally arranged. The method includes: an absorption layerformation step of growing an absorption layer on a first conductivitytype group III-V semiconductor substrate; a window layer formation stepof growing a window layer on the absorption layer, which window layer iscomposed of a compound semiconductor including P, and has a band gapenergy greater than a band gap energy of the absorption layer; and animpurity diffusion step of diffusing a second conductivity type impurityin regions, in the window layer, corresponding to the plurality ofabsorption regions. In the window layer formation step, the window layeris grown by metal-organic vapor phase epitaxy using only metal-organicsources, and a growth temperature of the window layer is equal to orlower than a growth temperature of the absorption layer.

In the method for manufacturing a photodiode array according to thepresent invention, a window layer composed of a compound semiconductorincluding P is grown on the absorption layer. As compared to the casewhere an InGaAs layer is provided as a window layer (Non-Patent Document1), the window layer composed of a compound semiconductor including Pallows electrodes and a passivation layer to be favorably formedthereon, and thus dark current at the crystal surface is reduced.Further, in the window layer formation step, the window layer is grownby metal-organic vapor phase epitaxy (MOVPE) using only metal-organicsources, and the growth temperature of the window layer is equal to orlower than that of the absorption layer. In the MOVPE using onlymetal-organic sources, tertiarybutylphosphine (TBP) or the like, whichis an organic metal, is used as a raw material for P. Therefore, evenwhen the growth temperature of the window layer is reduced as comparedto that of the ordinary MOVPE using phosphine, the crystallinity of thewindow layer is not degraded, and thus excellent device characteristicsare obtained. In addition, since the growth temperature of the windowlayer is equal to or lower than that of the absorption layer, theabsorption layer is prevented from being affected by the growth of thewindow layer. Therefore, the crystalline quality of the absorption layeris maintained, and thus excellent characteristics are obtained.

In the above-described method for manufacturing a photodiode array, theabsorption layer may be grown by MOVPE using only metal-organic sourcesin the absorption layer formation step. Alternatively, the absorptionlayer may be grown by molecular beam epitaxy. According to theabove-described method for manufacturing a photodiode array, regardlessof whether the growth method of the absorption layer is the same as ordifferent from the growth method of the window layer, the absorptionlayer is prevented from being affected by the growth of the windowlayer. Therefore, the crystalline quality of the absorption layer ismaintained, and thus excellent characteristics are obtained.

In the above-described method for manufacturing a photodiode array, thegrowth temperature of the window layer may be equal to or higher than400° C. but lower than 600° C. When the growth temperature of the windowlayer is lower than 600° C., the crystalline quality of the absorptionlayer can be favorably maintained even if the absorption layer includesa material, such as GaAsSb, that is not resistant to heat. When thegrowth temperature of the window layer is lower than 400° C., thecrystalline quality of the window layer cannot be maintained favorablyalthough the degree of surface defects is lessened, which causes adifficulty in obtaining excellent device characteristics.

A first photodiode array according to the present invention has aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, and includes: an absorption layer disposed on a firstconductivity type group III-V semiconductor substrate; and a windowlayer disposed on the absorption layer, which window layer is composedof a compound semiconductor including P, has a band gap energy greaterthan a band gap energy of the absorption layer, and includes a secondconductivity type impurity being diffused in regions thereofcorresponding to the plurality of absorption regions. The percentage ofdefective absorption regions among the plurality of absorption regions,which are caused by surface defects of the window layer, is equal to orgreater than 0.03% but not greater than 2%.

The percentage of defective absorption regions means the percentage ofabsorption regions, among the plurality of absorption regions, which donot function as photodiodes due to dark current failure and/orsensitivity failure. Since the percentage of defective absorptionregions is equal to or greater than 0.03%, the growth temperature of thewindow layer need not be set at a high temperature such as 660° C. ormore as in Non-Patent Document 3 in order to reduce surface defects ofthe window layer. Accordingly, the absorption layer is prevented frombeing affected by the growth of the window layer, and thus thecrystalline quality of the absorption layer is maintained, resulting inexcellent characteristics. In addition, focusing onto the wafer surfaceis facilitated, which makes it easy to perform surface inspection anddevice fabrication. Since the percentage of defective absorption regionsis not greater than 2%, sufficient characteristics are obtained forapplications of the photodiode array to cameras or the like.

A second photodiode array according to the present invention has aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, and includes: an absorption layer disposed on a firstconductivity type group III-V semiconductor substrate; and a windowlayer disposed on the absorption layer, which window layer is composedof a compound semiconductor including P, has a band gap energy greaterthan a band gap energy of the absorption layer, and includes a secondconductivity type impurity being diffused in regions thereofcorresponding to the plurality of absorption regions. The surface defectdensity of the window layer is equal to or greater than 50 cm⁻² but notgreater than 3000 cm⁻².

Since the surface defect density of the window layer is equal to orgreater than 50 cm⁻², the growth temperature of the window layer neednot be set at a high temperature such as 660° C. or more as inNon-Patent Document 3 in order to reduce surface defects of the windowlayer. In addition, when manufacturing the photodiode array, excessivecontrol for the epitaxial wafer having the absorption layer and thewindow layer grown on the group III-V semiconductor substrate is notrequired, resulting in a reduction in manufacturing cost. Further,focusing onto the wafer surface is facilitated, which makes it easy toperform wafer surface inspection and device fabrication. Utilizing this,screening inspection for defective wafers based on the density range isrealized. Since the surface defect density of the window layer is notgreater than 3000 cm⁻², sufficient characteristics are obtained forapplications of the photodiode array to cameras or the like.

A third photodiode array according to the present invention has aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, and includes: an absorption layer disposed on a firstconductivity type group III-V semiconductor substrate; and a windowlayer disposed on the absorption layer, which window layer is composedof a compound semiconductor including P, has a band gap energy greaterthan a band gap energy of the absorption layer, and includes a secondconductivity type impurity being diffused in regions thereofcorresponding to the plurality of absorption regions. The average areaof surface defects of the window layer is equal to or greater than 3 μm²but not greater than 800 μm².

Since the average area of surface defects of the window layer is equalto or greater than 3 μm², the growth temperature of the window layerneed not be set at a high temperature such as 660° C. or more in orderto reduce surface defects of the window layer. Accordingly, theabsorption layer is prevented from being affected by the growth of thewindow layer, and thus the crystalline quality of the absorption layeris maintained, resulting in excellent characteristics. Further, focusingonto the wafer surface is facilitated, which makes it easy to performwafer surface inspection and device fabrication. Utilizing this,screening inspection for defective wafers based on the density range isrealized. Since the average area of surface defects of the window layeris not greater than 800 μm², sufficient characteristics are obtained forapplications of the photodiode array to cameras or the like.

In the first to third photodiode arrays, each of the surface defects ofthe window layer has a concave or convex shape having a height of 10 nmor more.

In the above-described method for manufacturing a photodiode array, awindow layer composed of InP may be grown in the window layer formationstep. Likewise, in the above-described first to third photodiode arrays,the window layer may be composed of InP. Accumulation of technicalknowledge for forming a passivation layer on the surface of InP crystalis greater than that for forming a passivation layer on the surface ofInGaAs crystal. Therefore, dark current at the crystal surface can beeasily reduced. Further, when light comes in the absorption layerthrough the window layer, dark current can be effectively reduced whilepreventing absorption of near infrared light in a region on thelight-incoming side relative to the absorption layer.

In the above-described method for manufacturing a photodiode array, anabsorption layer having a multiple quantum well structure may be formedin the absorption layer formation step. Likewise, in the above-describedfirst to third photodiode arrays, the absorption layer may have amultiple quantum well structure. In the case where the absorption layerhas a multiple quantum well structure, if the window layer is grown at ahigh temperature, steepness of the interface between the well layer andthe barrier layer is degraded, which may cause a reduction in devicecharacteristics such as light-to-electricity conversion efficiency.However, according to the above-described photodiode array manufacturingmethod and photodiode arrays, even when the absorption layer has amultiple quantum well structure, the crystalline quality of theabsorption layer is maintained, and thus excellent characteristics areobtained.

In the above-described method for manufacturing a photodiode array, thegroup III-V semiconductor substrate may be an InP substrate, and anabsorption layer having a multiple quantum well structure may be formedin the absorption layer formation step by alternately growing layersincluding InGaAs and layers including GaAsSb. Likewise, in theabove-described first to third photodiode arrays, the group III-Vsemiconductor substrate may be an InP substrate, and the absorptionlayer may have a multiple quantum well structure in which layersincluding InGaAs and layers including GaAsSb are alternately laminated.In the case where the absorption layer has such a structure, if thewindow layer is grown at a high temperature, steepness of the interfacebetween the GaAsSb layer and the InGaAs layer is degraded because GaAsSbis not resistant to heat, which may cause a deterioration of devicecharacteristics. However, according to the above-described photodiodearray manufacturing method and photodiode arrays, even when theabsorption layer has the multiple quantum well structure in which layersincluding InGaAs and layers including GaAsSb are alternately laminated,the crystalline quality of the absorption is maintained, and thusexcellent characteristics are obtained.

In the above-described method for manufacturing a photodiode array, themultiple quantum well structure of the absorption layer may be formed inthe absorption layer formation step by alternately growingIn_(x)Ga_(1-x)As (0.38≦x≦0.68) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62), or byalternately growing Ga_(1-u)In_(u)N_(v)As_(1-v) (0.4≦u≦0.8, 0<v≦0.2) andGaAs_(1-y)Sb_(y) (0.36≦y≦0.62). Likewise, in the above-described firstto third photodiode arrays, the multiple quantum well structure of theabsorption layer may be composed of pairs of In_(x)Ga_(1-x)As(0.38≦x≦0.68) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62), or pairs ofGa_(1-u)In^(u)N_(v)As_(1-v) (0.4≦u≦0.8, 0<v≦0.2) and GaAs_(1-y)Sb_(y)(0.36≦y≦0.62). Thereby, a large number of absorption regions 21, such asphotodiodes, each having responsivity in the near infrared region can bemanufactured with efficiency while maintaining excellent crystallinity.

In order to solve the above-described problems, the present inventionprovides a method for manufacturing an epitaxial wafer which is used formanufacturing a photodiode array having a plurality of absorptionregions arranged one-dimensionally or two-dimensionally. The methodincludes: an absorption layer formation step of growing an absorptionlayer on a first conductivity type group III-V semiconductor substrate;and a window layer formation step of growing a window layer on theabsorption layer, which window layer is composed of a compoundsemiconductor including P, and has a band gap energy greater than a bandgap energy of the absorption layer. In the window layer formation step,the window layer is grown by metal-organic vapor phase epitaxy usingonly metal-organic sources, and a growth temperature of the window layeris equal to or lower than a growth temperature of the absorption layer.

In the method for manufacturing an epitaxial wafer according to thepresent invention, like the above-described method for manufacturing aphotodetector array, a window layer composed of a compound semiconductorincluding P is grown on the absorption layer. Therefore, electrodes anda passivation layer can be favorably formed on the window layer, andthus dark current at the crystal surface is reduced. Further, in thewindow layer formation step, the window layer is grown by MOVPE usingonly metal-organic sources, at a growth temperature equal to or lowerthan that of the absorption layer. Therefore, the absorption layer isprevented from being affected by the growth of the window layer, andthus the crystalline quality of the absorption layer is maintained,resulting in excellent characteristics.

In the above-described method for manufacturing an epitaxial wafer, theabsorption layer may be grown by MOVPE using only metal-organic sourcesin the absorption layer formation step. Alternatively, the absorptionlayer may be grown by molecular beam epitaxy. According to theabove-described method for manufacturing an epitaxial wafer, regardlessof whether the growth method of the absorption layer is the same as ordifferent from the growth method of the window layer, the absorptionlayer is prevented from being affected by the growth of the windowlayer. Therefore, the crystalline quality of the absorption layer ismaintained, and thus excellent characteristics are obtained.

In the above-described method for manufacturing an epitaxial wafer, thegrowth temperature of the window layer may be equal to or higher than400° C. but lower than 600° C. When the growth temperature of the windowlayer is lower than 600° C., the crystalline quality of the absorptionlayer can be favorably maintained even if the absorption layer includesa material, such as GaAsSb, that is not resistant to heat. When thegrowth temperature of the window layer is lower than 400° C., thecrystalline quality of the window layer cannot be maintained favorablyalthough the degree of surface defects is lessened, which causes adifficulty in obtaining excellent device characteristics.

A first epitaxial wafer according to the present invention is anepitaxial wafer used for manufacturing a photodiode array having aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, and the epitaxial wafer includes: an absorption layerdisposed on a first conductivity type group III-V semiconductorsubstrate; and a window layer disposed on the absorption layer, whichwindow layer is composed of a compound semiconductor including P, andhas a band gap energy greater than a band gap energy of the absorptionlayer. The surface defect density of the window layer is equal to orgreater than 50 cm⁻² but not greater than 3000 cm⁻².

Since the surface defect density of the window layer is equal to orgreater than 50 cm⁻², the growth temperature of the window layer neednot be set at a high temperature such as 660° C. or more as inNon-Patent Document 3 in order to reduce surface defects of the windowlayer. Further, when manufacturing the photodiode array, excessivecontrol for the epitaxial wafer having the absorption layer and thewindow layer grown on the group III-V semiconductor substrate is notrequired, resulting in a reduction in manufacturing cost. Further,focusing onto the wafer surface is facilitated, which makes it easy toperform wafer surface inspection and device fabrication. Utilizing this,screening inspection for defective wafers based on the density range isrealized. Since the surface defect density of the window layer is notgreater than 3000 cm⁻², sufficient characteristics are obtained forapplications of the photodiode array to cameras or the like.

A second epitaxial wafer according to the present invention is anepitaxial wafer used for manufacturing a photodiode array having aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, and the epitaxial wafer includes an absorption layerdisposed on a first conductivity type group III-V semiconductorsubstrate; and a window layer disposed on the absorption layer, whichwindow layer is composed of a compound semiconductor including P, andhas a band gap energy greater than a band gap energy of the absorptionlayer. The average area of surface defects of the window layer is equalto or greater than 3 μm² but not greater than 800 μm².

Since the average area of surface defects of the window layer is equalto or greater than 3 μm², the growth temperature of the window layerneed not be set at a high temperature such as 660° C. or more as inNon-Patent Document 3 in order to reduce surface defects of the windowlayer. Accordingly, the absorption layer is prevented from beingaffected by the growth of the window layer, and thus the crystallinequality of the absorption layer is maintained, resulting in excellentcharacteristics. Further, focusing onto the wafer surface isfacilitated, which makes it easy to perform wafer surface inspection anddevice fabrication. Utilizing this, screening inspection for defectivewafers based on the density range is realized. Since the average area ofsurface defects of the window layer is not greater than 800 μm²,sufficient characteristics are obtained for applications of thephotodiode array to cameras or the like.

In the first and second epitaxial wafers, each of the surface defects ofthe window layer has a concave or convex shape having a height of 10 nmor more.

According to the present invention, it is possible to provide: aphotodiode array and its manufacturing method, which can maintain thecrystalline quality of an absorption layer formed on a group III-Vsemiconductor substrate to realize excellent characteristics, and whichcan improve the crystallinity at the surface of a window layer; anepitaxial wafer used for manufacturing of the photodiode array; and amethod for manufacturing the epitaxial wafer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an enlarged view showing a part of a structure of a photodiodearray 1 according to an embodiment of the present invention;

FIG. 2 is a diagram showing a structure of an MOVPE apparatus 100 usedfor manufacturing the photodiode array 1;

FIG. 3 is a flowchart showing process steps for manufacturing thephotodiode array 1 using the MOVPE apparatus 100;

FIG. 4 is a diagram showing a structure of an epitaxial wafer 27;

FIGS. 5A to 5C are diagrams showing examples of variations in thecrystal growth temperatures when an absorption layer 7 b, a diffusionconcentration adjusting layer 9 b, and a window layer 11 b aresuccessively grown;

FIG. 6 is a graph showing the relation between the diameter (μm) ofsurface defects of a window layer 11 (11 b), and the percentage ofdefective absorption regions, among absorption regions 21, caused bysurface defects of the window layer 11 (11 b);

FIG. 7 is a diagram showing the surface defect density of the windowlayer 11 (11 b), the average area of surface defects, the percentage ofdefective absorption regions, among the absorption regions 21, caused bysurface defects, the dark current, and the dark current density, whichdepend on the growth temperature of the window layer 11 (11 b);

FIG. 8A is a graph showing the relation between the surface defectdensity of the window layer 11 and the percentage of defectiveabsorption regions among the absorption regions 21, and FIG. 8B is agraph showing the relation between the average area of surface defectsof the window layer 11 and the percentage of defective absorptionregions among the absorption regions 21; and

FIG. 9 is a diagram showing the correlations, in the photodiode array 1,among the number of runs from reactor cleaning, the surface defectdensity, the average area of surface defects, the percentage ofdefective absorption regions among the absorption regions 21, the darkcurrent, and the dark current density.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the drawings. In the descriptionof drawings, if possible, the same elements are represented by the samereference numerals, and duplication of description is avoided.

FIG. 1 is an enlarged view showing a part of the structure of aphotodiode array 1 according to an embodiment of the present invention.The photodiode array 1 includes a plurality of absorption regions (alsoreferred to as pixels) arranged one-dimensionally or two-dimensionally.The photodiode array 1 further includes a substrate 3, a semiconductorlayer 5, an absorption layer 7, a diffusion concentration adjustinglayer 9, a window layer 11, a passivation layer (insulating layer) 13, aplurality of p-type (second conductivity type) electrodes 15, and ann-type (first conductivity type) electrode 17.

The substrate 3 is a group III-V semiconductor substrate of the presentembodiment, and is composed of InP, for example. The substrate 3 isSi-doped, and has an n-type conductivity. A buffer layer (not shown) onthe substrate 3 is composed of n-type InP, and has a thickness of about10 nm. The semiconductor layer 5 is disposed on the substrate 3 with thebuffer layer intervening therebetween, and the buffer layer is incontact with the rear surface of the semiconductor layer 5. Thesemiconductor layer 5 is composed of n-type InGaAs, and has a thicknessof about 150 nm.

The absorption layer 7 is disposed on the surface of the semiconductorlayer 5, and the diffusion concentration adjusting layer 9 is disposedon the absorption layer 7. The rear surface of the diffusionconcentration adjusting layer 9 is in contact with the absorption layer7. The absorption layer 7 is disposed between the semiconductor layer 5and the diffusion concentration adjusting layer 9 (in other words, theabsorption layer 7 is disposed between the substrate 3 and the diffusionconcentration adjusting layer 9). The absorption layer 7 of the presentembodiment has a multiple quantum well structure in which a plurality ofquantum well layers and a plurality of barrier layers are alternatelylaminated.

For example, the absorption layer 7 may have a type-II multiple quantumwell structure in which a plurality of InGaAs layers and a plurality ofGaAsSb layers, which are included in the absorption layer 7, arealternately laminated. The absorption layer 7 includes, for example, 250pairs of the InGaAs layers and the GaAsSb layers. The thickness of eachInGaAs layer is about 5 nm, and the thickness of each GaAsSb layer isalso about 5 nm. The specific compositions of the InGaAs layer and theGaAsSb layer in the absorption layer 7 are In_(x)Ga_(1-x)As(0.38≦x≦0.68) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62), respectively. Theabsorption layer 7 may include 250 pairs of Ga_(1-t)In_(t)N_(u)As_(1-u)(0.4≦t≦0.8, 0<u≦0.2) and GaAs_(1-v)Sb_(v) (0.36≦v≦0.62). When theabsorption layer 7 has the compositions as described above, a largenumber of absorption regions 21, such as photodiodes, each havingresponsivity in the near infrared region can be manufactured withefficiency while maintaining excellent crystallinity.

The diffusion concentration adjusting layer 9 is disposed between theabsorption layer 7 and the window layer 11. The window layer 11 isdisposed on the diffusion concentration adjusting layer 9, and thesurface of the diffusion concentration adjusting layer 9 is in contactwith the rear surface of the window layer 11. The passivation layer 13is disposed on the surface of the window layer 11, and the passivationlayer 13 has openings. A plurality of p-type electrodes 15 are disposedon the surface of the window layer 11, and contact the surface of thewindow layer 11.

The diffusion concentration adjusting layer 9 is composed of InGaAs thatis a group III-V semiconductor, and has a thickness of about 1.0 μm. Thediffusion concentration adjusting layer 9 is undoped. The window layer11 is composed of a compound semiconductor including P, for example, InPthat is a group III-V semiconductor, and has a thickness of about 0.8μm. The window layer 11 has a band gap energy greater than those of theabsorption layer 7 and the diffusion concentration adjusting layer 9.The window layer 11 is doped with Si which is an n-type dopant.

A semiconductor region consisting of the diffusion concentrationadjusting layer 9 and the window layer 11 includes a region 19 and aplurality of absorption regions 21. Each of the plurality of absorptionregions 21 has sides that abut the region 19. Each of the plurality ofabsorption regions 21 is formed of an impurity diffusion region 25, andthe impurity diffusion region 25 is doped with a predetermined impurityelement (Zn in the present embodiment).

Each of the plurality of p-type electrodes 15 is disposed on a region,in the window layer 11, corresponding to the impurity diffusion region25 forming each absorption region 21 so as to be placed in the openingof the passivation layer 13. The p-type electrode 15 is in ohmic contactwith the window layer 11. The n-type electrode 17 is disposed on therear surface of the substrate 3, and is in contact with the rearsurface. The n-type electrode 17 is in ohmic contact with the substrate3. The n-type electrode 17 is common to all the absorption regions 21.

Hereinafter, a method for manufacturing the photodiode array 1 will bedescribed. FIG. 2 is a diagram showing the structure of an MOVPEapparatus 100 used for the manufacturing method of the presentembodiment. The MOVPE apparatus 100 includes a reactor 101, and first tothird raw material supply sources 102, 103, and 104 for supplying rawmaterials to the reactor 101. The reactor 101 is a so-called horizontalreactor having a quartz flow-channel 105 in which a flow path is formedin the horizontal direction. The substrate 3 is put on a susceptor 107having a heater 106. The susceptor 107 rotatably supports the substrate3.

The first raw material supply source 102 contains, for example,triethylgallium (TEGa), trimethylaluminum (TMAl), and trimethylindium(TMIn) which are organic metals, as raw materials for Ga, Al, and Inwhich are group III elements, respectively. The second raw materialsupply source 103 contains, for example, tertiarybutylarsine (TBAs),tertiarybutylphosphine (TBP), and trimethylantimony (TMSb) which areorganic metals, as raw materials for As, P, and Sb which are group Velements, respectively. The third raw material supply source 104contains, for example, tetraethylsilane (TeESi), which is an organicmetal, as an n-type dopant.

These organic metals are turned into gases and transferred, togetherwith carrier gases (H₂, N₂), to the reactor 101 from the first rawmaterial supply source 102, the second raw material supply source 103,and the third raw material supply source 104. The flow rates of therespective organic metal gases are controlled by mass flow controllers(MFCs) 109 a to 109 f. Further, a vacuum pump 110 and a scrubber 111 areattached to the outlet of the reactor 101.

Using the MOVPE apparatus 100, the photodiode array 1 of the presentembodiment is manufactured in accordance with a manufacturing processshown in FIG. 3. Initially, an epitaxial wafer 27 shown in FIG. 4 ismanufactured by metal-organic vapor phase epitaxy using onlymetal-organic sources. First, an Si-doped substrate 3 b is prepared. Ona main surface of the substrate 3 b, an n-type doped InP buffer layer(not shown) is grown to a thickness of 10 nm. On the buffer layer, ann-type impurity doped InGaAs semiconductor layer 5 b is grown to athickness of 150 nm. On the semiconductor layer 5 b, an absorption layer7 b having an InGaAs—GaAsSb type-II multiple quantum well structure isgrown (absorption layer formation step S1). In the multiple quantum wellstructure, an undoped InGaAs layer having a thickness of 5 nm and anundoped GaAsSb layer having a thickness of 5 nm are successivelydisposed from the substrate side, and this double-layer structure isrepeated 250 times. The specific compositions of the InGaAs layer andthe GaAsSb layer in the absorption layer 7 b are In_(x)Ga_(1-x)As(0.38≦x≦0.68) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62), respectively. Theabsorption layer 7 b may include 250 pairs ofGa_(1-t)In_(t)N_(u)As_(1-u) (0.4≦t≦0.8, 0<u≦0.2) and GaAs_(1-v)Sb_(v)(0.36≦v≦0.62).

The crystal growth temperatures for all the layers up to the formationof the absorption layer 7 b are, for example, equal to or higher than400° C. but not higher than 600° C. In the crystal growths of all thelayers up to the formation of the absorption layer 7 b, as raw materialgases, TEGa, TBAs, and TMSb are used for GaAsSb, and TEGa, TMIn, andTBAs are used for InGaAs.

Next, an InGaAs diffusion concentration adjusting layer 9 b is grown onthe absorption layer 7 b, and an InP window layer 11 b is grown on thediffusion concentration adjusting layer 9 b (window layer formation stepS2). At this time, TMIn and TBP are used as raw material gases for InP.In this way, TBP, which is an organic metal, is used as a raw materialfor P in the present embodiment. Since the decomposition temperature ofTBP is about 300° C. lower than that of phosphine (PH₃) which is ageneral raw material for P, the window layer 11 b can be grown at a lowtemperature. That is, in the present embodiment, the growth temperaturefor the window layer 11 b can be made equal to or lower than the growthtemperature of the absorption layer 7 b, preferably, equal to or higherthan 400° C. but lower than 600° C. In an example, the growthtemperature can be made 500° C.

When an InP window layer is grown at a growth temperature equal to orhigher than 400° C. but lower than 600° C. (for example, 500° C.) usingphosphine (PH₃), decomposition of phosphine is not sufficientlypromoted, and thereby the substantial V/III ratio becomes very small.Therefore, point defects such as P-vacancies occur, which causes adifficulty in achieving excellent device characteristics.

FIGS. 5A to 5C are diagrams showing examples of variations in thecrystal growth temperatures when the absorption layer 7 b, the diffusionconcentration adjusting layer 9 b, and the window layer 11 b aresuccessively grown. In a growth temperature pattern (hereinafterreferred to as pattern A) shown in FIG. 5A, the absorption layer 7 b,the diffusion concentration adjusting layer 9 b, and the window layer 11b are grown at the same temperature (e.g., 450° C.). In a growthtemperature pattern (hereinafter referred to as pattern B) shown in FIG.5B, the absorption layer 7 b is grown at a relatively high temperature(e.g., 500° C.), and the diffusion concentration adjusting layer 9 b andthe window layer 11 b are grown at a temperature (e.g., 450° C.) lowerthan that of the absorption layer 7 b. In a growth temperature pattern(hereinafter referred to as pattern C) shown in FIG. 5C, the absorptionlayer 7 b and the diffusion concentration adjusting layer 9 b are grownat a relatively high temperature (e.g., 500° C.), and the window layer11 b is grown at a temperature (e.g., 450° C.) lower than that of theabsorption layer 7 b.

In pattern B, since the absorption layer 7 b is grown at the relativelyhigh temperature, the crystalline quality is improved as compared topattern A, and thereby dark current is reduced. In pattern C, since theabsorption layer 7 b and the diffusion concentration adjusting layer 9 bare grown at the relatively high temperature, the crystalline quality ismore improved than in pattern B, and thereby dark current is morereduced.

After the epitaxial wafer 27 is manufactured through the above-describedsteps, manufacturing of the photodiode array 1 is performed using theepitaxial wafer 27. First, p-type regions (corresponding to the impuritydiffusion regions 25 of the photodiode array 1), which extend from thesurface of the window layer 11 b to the diffusion concentrationadjusting layer 9 b, are formed by diffusing an impurity into regions,in the window layer 11 b, corresponding to the plurality of absorptionregions 21 (impurity diffusion step S3). Specifically, a selectivediffusion mask pattern of an SiN layer (the passivation layer 13) isformed on the window layer 11 b, and a p-type impurity, Zn, isselectively diffused from the openings of the mask pattern, therebyforming the p-type regions.

Thereafter, on the parts of the surface of the window layer 11 bcorresponding to the p-type regions, p-type electrodes 15 composed ofAuZn are provided so as to be in ohmic contact with the window layer 11b. Further, on the rear surface of the substrate 3 b, an n-typeelectrode 17 composed of AuGeNi is provided so as to be in ohmic contactwith the substrate 2 b (electrode formation step S4). Through theabove-described steps, the photodiode array 1 is manufactured using theepitaxial wafer 27.

The substrate 3, the semiconductor layer 5, the absorption layer 7, thediffusion concentration adjusting layer 9, and the window layer 11 ofthe photodiode array 1 are parts of the substrate 3 b, the semiconductorlayer 5 b, the absorption layer 7 b, the diffusion concentrationadjusting layer 9 b, and the window layer 11 b of the epitaxial wafer27, respectively.

The following will describe the effects achieved by the photodiode array1 and the manufacturing method thereof, and the epitaxial wafer 27 andthe manufacturing method thereof according to the present embodiment.

In the above-described manufacturing methods for the photodiode array 1and the epitaxial wafer 27, the window layer 11 b composed of a compoundsemiconductor including P is grown on the absorption layer 7 b.Therefore, as compared to the case where an InGaAs layer is provided asa window layer (Non-Patent Document 1), the window layer 11 b composedof a compound semiconductor including P allows the p-type electrodes 15and a passivation layer 13 to be favorably formed thereon, and thus darkcurrent at the crystal surface is reduced.

Further, in the above-described manufacturing methods for the photodiodearray 1 and the epitaxial wafer 27, in the window layer formation step,the window layer 11 b is grown by the MOVPE using only metal-organicsources, and the growth temperature of the window layer 11 b is equal toor lower than the growth temperature of the absorption layer 7 b. TheMOVPE using only metal-organic sources adopts, for example, TBP which isan organic metal, as a raw material for P. Therefore, as compared to theordinary MOVPE using phosphine, favorable crystal growth is realizedeven when the growth temperature of the window layer 11 b is lowered,and thus the crystallinity at the surface of the window layer 11 b isimproved. When the growth temperature of the window layer 11 b is equalto or lower than the growth temperature of the absorption layer 7 b, theabsorption layer 7 b is prevented from being affected by the growth ofthe window layer 11 b, and thus the crystalline quality of theabsorption layer 7 b is maintained, resulting in excellentcharacteristics.

Further, as in the present embodiment, the absorption layer may begrown, in the absorption layer formation step, by the same MOVPE usingonly metal-organic sources as that for the window layer. Even in thiscase, the above-described manufacturing methods for the photodiode array1 and the epitaxial wafer 27 can prevent the absorption layer 7 b frombeing affected by the growth of the window layer 11 b, and can maintainthe crystalline quality of the absorption layer 7 b, resulting inexcellent characteristics. In addition, if the layers from theabsorption layer 7 b to the window layer 11 b are continuously grown bythe MOVPE using only metal-organic sources, no regrown interface occursbetween the absorption layer 7 b and the window layer 11 b, and thusincorporation of impurities such as O, C, and H can be avoided. Forexample, the concentrations of O, C, and H can be made less than 1×10¹⁷cm⁻³. Accordingly, the crystalline quality of the absorption layer 7 canbe maintained while sufficiently reducing surface defects of the windowlayer 11 b.

Further, as in the present embodiment, it is preferable that the growthtemperature of the window layer 11 b be equal to or higher than 400° C.but lower than 600° C. When the growth temperature of the window layer11 b is lower than 600° C., the crystalline quality of the absorptionlayer 7 b can be favorably maintained even if the absorption layer 7 bincludes a material such as GaAsSb that is not resistant to heat. Whenthe growth temperature of the window layer 11 b is lower than 400° C.,the degree of surface defect is lessened, but the crystalline quality ofthe window layer 11 b cannot be favorably maintained, which causes adifficulty in realizing excellent device characteristics.

The following Table 1 shows the relations among the growth temperatureof the window layer 11 b, the crystalline qualities of the absorptionlayer 7 b and the window layer 11 b, and the surface defects. It isfound from Table that, when the growth temperature of the window layer11 b is equal to or higher than 400° C. but lower than 600° C., bothimprovement of crystalline qualities of the absorption layer 7 b and thewindow layer 11 b and reduction in surface defects can be achieved. Inthe present embodiment, the surface defects of the window layer 11 brefer to defects each having a concave or convex shape of a height of 10nm or more.

TABLE 1 Growth temperature Crystalline quality Crystalline quality ofInP window layer of absorption layer of window layer Surface defectLower than 400° C. ◯ X ◯ Good 400° C. or higher but ◯ ◯ Δ lower than600° C. Good Good Surface defect occurs but its (present embodiment)area decreases with reduction in growth temperature 600° C. or higherbut X ◯ X lower than 660° C. Degraded by heat Good Surface defect havinglarge area occurs 600° C. or higher X ◯ ◯ Degraded by heat Good Surfacedefect free

Further, as in the present embodiment, it is preferable that the windowlayer 11 b composed of InP be grown in the window formation step. Thatis, it is preferable that, in the photodiode array 1, the window layer11 be composed of InP. The reason is as follows. Accumulation oftechnical knowledge for the technique of forming a passivation layer onthe surface of InP crystal is greater than that for the technique offorming a passivation layer on the surface of InGaAs crystal, andtherefore, dark current at the crystal surface can be easily reduced.Further, when light comes in the absorption layer 7 through the windowlayer 11, dark current can be effectively reduced while preventingabsorption of near infrared light in a region on the light-incoming siderelative to the absorption layer 7.

Further, as in the present embodiment, it is preferable that theabsorption layer 7 b having a multiple quantum well structure be formedin the absorption layer formation step. That is, it is preferable that,in the photodiode array 1 and the epitaxial wafer 27, the absorptionlayer 7 (7 b) have a multiple quantum well structure. In the case wherethe absorption layer 7 (7 b) has a multiple quantum well structure, ifthe window layer 11 (11 b) is grown at a high temperature, steepness ofthe interface between the well layer and the barrier layer is degraded,which may cause degradation of device characteristics such aslight-to-electricity conversion efficiency. However, according to theabove-described photodiode array 1 and manufacturing method thereof,even if the absorption layer 7 (7 b) has a multiple quantum wellstructure, the crystalline quality of the absorption layer 7 (7 b) ismaintained, and thus excellent characteristics can be obtained.

Further, as in the present embodiment, it is more preferable that thesubstrate 3 b be an InP substrate, and the absorption layer 7 b having amultiple quantum well structure be formed in the absorption layerformation step by alternately growing layers including InGaAs and layersincluding GaAsSb. Likewise, it is more preferable that, in thephotodiode array 1 and the epitaxial wafer 27, the substrate 3 (3 b) bean InP substrate, and the absorption layer 7 (7 b) has a multiplequantum well structure in which layers including InGaAs and layersincluding GaAsSb are alternately laminated. In the case where theabsorption layer 7 (7 b) has such a structure, if the window layer 11(11 b) is grown at a high temperature, steepness of the interfacebetween the GaAsSb layer and the InGaAs layer is reduced because GaAsSbis not resistant to heat, and thereby device characteristics are likelyto be degraded. However, according to the above-described photodiodearray 1 and manufacturing method thereof, even if the absorption layer 7(7 b) has a multiple quantum well structure in which layers includingInGaAs and layers including GaAsSb are alternately laminated, thecrystalline quality of the absorption layer 7 (7 b) is maintained, andthus excellent characteristics can be obtained.

In the InGaAs/GaAsSb type-II multiple quantum well structure asdescribed in the present embodiment, since the compound semiconductorshaving different compositions are alternately laminated a plurality oftimes, it is difficult to control the compositions, and strain due tolattice mismatch with the substrate is likely to be accumulated.Particularly when the number of pairs of quantum well layers and barrierlayers is extremely great, such as 250 pairs or more, strain due tolattice mismatch is more likely to be accumulated. Due to such strain,surface defects are likely to occur in the window layer. Accordingly, inthe photodiode array having the type-II quantum well structure, surfacedefects are likely to occur in the window layer. In order to reduce suchsurface defects, it has conventionally been necessary to grow the windowlayer at a high growth temperature. However, according to the photodiodearray 1 of the present embodiment and manufacturing method thereof, evenwhen the photodiode array 1 has such a structure, the crystallinequality of the absorption layer 7 b can be maintained by reducing thegrowth temperature of the window layer 11 b, and thus excellentcharacteristics can be obtained.

FIG. 6 shows graphs representing the relation between the diameter (μm)of surface defects of the window layer 11 (11 b), and the percentage ofdefective absorption regions (hereinafter referred to as percentage ofdefective pixels) among the absorption regions 21, which are caused bysurface defects of the window layer 11 (11 b). In FIG. 6, graphs G1 toG3 represent the cases where the surface defect density is 1000 cm⁻²,2000 cm⁻², and 3000 cm⁻², respectively. The percentage of defectivepixels is calculated according to the following Eq. 1. In Eq. 1, Drepresents the surface defect density (cm⁻²), and R represents thesurface defect size (μmφ). It is assumed that the pixel interval is 30μm, and the pixel size (including impurity diffusion region) is 19 μm.

$\begin{matrix}\begin{matrix}\mspace{490mu} & {{Equation}\mspace{14mu} 1}\end{matrix} \\\begin{matrix}{( {{percentage}\mspace{14mu} {of}\mspace{14mu} {defective}\mspace{14mu} {pixels}}\mspace{14mu} ) = {\frac{( {{defect}\mspace{14mu} {density}} )}{( {{pixel}\mspace{14mu} {density}} )} \times}} \\{\begin{pmatrix}{{probability}\mspace{14mu} {that}\mspace{14mu} {detects}} \\{{overlap}\mspace{14mu} {pixels}}\end{pmatrix}} \\{= {\frac{D}{( {30 \times 10^{- 4}} )^{- 2}} \times ( \frac{\pi \times ( {\frac{19}{2} + \frac{R}{2}} )^{2}}{30 \times 30} )}}\end{matrix}\end{matrix}$

It is found from FIG. 6 that, when the surface defect density is 2000cm⁻² and the surface defect size is 20 μmφ, the percentage of defectivepixels is 2.4%.

FIG. 7 is a diagram representing the surface defect density of thewindow layer 11 (11 b), the average area of surface defects, thepercentage of defective pixels due to surface defects, the dark current,and the dark current density, which depend on the growth temperature ofthe window layer 11 (11 b). FIG. 8A is a graph showing the relationbetween the surface defect density of the window layer 11 and thepercentage of defective pixels. FIG. 8B is a graph showing the relationbetween the average area of surface defects of the window layer 11 andthe percentage of defective pixels. FIG. 8A shows the case where thesurface defect density is 1000 cm⁻², and FIG. 8B shows the case wherethe average area of surface defects is 78.5 μm² (10 μmφ).

With reference to FIG. 7, as the growth temperature of the window layer11 (11 b) is lowered, the average area of surface defects becomessmaller, and the percentage of defective pixels decreases as shown inFIG. 8B. Further, as the average area of the surface defects becomessmaller, the dark current and the dark current density decrease. Inparticular, when the growth temperature of the window layer 11 (11 b) is525° C. or lower, the average area of surface defects of the windowlayer 11 (11 b) is reduced to a preferable value such as 750 μm² orless, and the percentage of defective pixels caused by surface defectsis reduced to a practical value such as 1.9% or less.

As described above, in the photodiode array 1 manufactured by themanufacturing method according to the present embodiment, the percentageof defective pixels caused by surface defects of the window layer 11 is2% or less, and the average area of surface defects is 800 μm² or less.Since the percentage of defective pixels is 2% or less, sufficientcharacteristics are obtained for applications of the photodetector array1 to cameras or the like. Further, since the average area of surfacedefects of the window layer is 800 μm² or less, sufficiently lowpercentage of defective pixels is obtained for applications of thephotodiode array to cameras or the like.

In the photodiode array 1, it is preferable that the percentage ofdefective pixels caused by surface defects of the window layer 11 be0.03% or more. When the percentage of defective pixels is 0.03% or more,the growth temperature of the window layer 11 need not be set at a hightemperature such as 660° C. or more in order to reduce surface defectsof the window layer 11. Accordingly, the absorption layer 7 is preventedfrom being affected by the growth of the window layer 11, and thus thecrystalline quality of the absorption layer 7 is maintained, resultingin excellent characteristics.

In the photodiode array 1 and the epitaxial wafer 27, it is preferablethat the surface defect density of the window layer 11 (11 b) be equalto or greater than 50 cm⁻² but not greater than 3000 cm⁻². When thesurface defect density of the window layer 11 (11 b) is equal to orgreater than 50 cm⁻², the growth temperature of the window layer 11 (11b) need not be set at a high temperature such as 660° C. or more inorder to reduce the surface defect of the window layer 11 (11 b). Inaddition, when manufacturing the photodiode array 1, excessive controlfor the epitaxial wafer 27 having the absorption layer 7 b and thewindow layer 11 b grown on the substrate 3 b is not required, and thusthe manufacturing cost can be reduced. Further, when the surface defectdensity of the window layer 11 is not greater than 3000 cm⁻², sufficientcharacteristics are obtained for applications of the photodiode array tocameras or the like.

Further, in the photodiode array 1 and the epitaxial wafer 27, it ispreferable that the average area of surface defects of the window layer11 (11 b) be 3 μm² or more. Thereby, the growth temperature of thewindow layer 11 (11 b) need not be set at a high temperature such as660° C. or more in order to reduce surface defects of the window layer11 (11 b). Accordingly, the absorption layer 7 (7 b) is prevented frombeing affected by the growth of the window layer 11 (11 b), and thus thecrystalline quality of the absorption layer 7 is maintained, resultingin excellent characteristics.

FIG. 9 is a diagram showing the correlations among the number of runsfrom reactor cleaning, the surface defect density, the average area ofsurface defects, the percentage of defective pixels, the dark current,and the dark current density, in the photodiode array 1 manufactured bythe above-described manufacturing method (i.e., the method in which theabsorption layer 7 b, the diffusion concentration adjusting layer 9 b,and the window layer 11 b are consistently grown by the MOVPE using onlymetal-organic sources). As shown in FIG. 9, as the number of runs fromreactor cleaning increases, the surface defect density increases. Whenthe number of runs from reactor cleaning is 40 or less, the surfacedefect density of the window layer 11 (11 b) is reduced to a preferablevalue such as 3000 cm⁻² or less, and the percentage of defective pixelscaused by surface defects is reduced to a practical value such as 2.0%or less.

In the above-described method for manufacturing the photodiode array 1,the absorption layer 7 b is grown by the MOVPE using only metal-organicsources in the absorption layer formation step. However, in thephotodiode array manufacturing method of the present invention, theabsorption layer may be grown by molecular beam epitaxy in theabsorption layer formation step. Also in this case, according to thephotodiode array manufacturing method of the present invention, theabsorption layer is prevented from being affected by the growth of thewindow layer, and thus the crystalline quality of the absorption layeris maintained, resulting in excellent characteristics.

1. A method for manufacturing a photodiode array having a plurality ofabsorption regions that are one-dimensionally or two-dimensionallyarranged, the method comprising: an absorption layer formation step ofgrowing an absorption layer on a first conductivity type group III-Vsemiconductor substrate; a window layer formation step of growing awindow layer on the absorption layer, the window layer being composed ofa compound semiconductor including P, and having a band gap energygreater than a band gap energy of the absorption layer; and an impuritydiffusion step of diffusing a second conductivity type impurity inregions, in the window layer, corresponding to the plurality ofabsorption regions; wherein in the window layer formation step, thewindow layer is grown by metal-organic vapor phase epitaxy using onlymetal-organic sources, and a growth temperature of the window layer isequal to or lower than a growth temperature of the absorption layer. 2.The method according to claim 1, wherein in the absorption layerformation step, the absorption layer is grown by metal-organic vaporphase epitaxy using only metal-organic sources.
 3. The method accordingto claim 1, wherein in the absorption layer formation step, theabsorption layer is grown by molecular beam epitaxy.
 4. The methodaccording to claim 1, wherein the growth temperature of the window layeris equal to or higher than 400° C. but lower than 600° C.
 5. The methodaccording to claim 1, wherein in the window layer formation step, thewindow layer composed of InP is grown.
 6. The method according to claim1, wherein in the absorption layer formation step, the absorption layerhaving a multiple quantum well structure is formed.
 7. The methodaccording to claim 6, wherein the group III-V semiconductor substrate isan InP substrate; and in the absorption layer formation step, theabsorption layer having a multiple quantum well structure is formed byalternately growing barrier layers including InGaAs and well layersincluding GaAsSb.
 8. The method according to claim 7, wherein in theabsorption layer formation step, the multiple quantum well structure ofthe absorption layer is formed by alternately growing In_(x)Ga_(1-x)As(0.38≦x≦0.68) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62), or by alternatelygrowing Ga_(1-u)In^(u)N_(v)As_(1-v) (0.4≦u≦0.8, 0<v≦0.2) andGaAs_(1-y)Sb_(y) (0.36≦y≦0.62).
 9. A photodiode array having a pluralityof absorption regions arranged one-dimensionally or two-dimensionally,the photodiode array comprising: an absorption layer disposed on a firstconductivity type group III-V semiconductor substrate; and a windowlayer disposed on the absorption layer, the window layer being composedof a compound semiconductor including P, having a band gap energygreater than a band gap energy of the absorption layer, and including asecond conductivity type impurity being diffused in regions thereofcorresponding to the plurality of absorption regions; wherein apercentage of defective absorption regions among the plurality ofabsorption regions, which are caused by surface defects of the windowlayer, is equal to or greater than 0.03% but not greater than 2%.
 10. Aphotodiode array having a plurality of absorption regions arrangedone-dimensionally or two-dimensionally, the photodiode array comprising:an absorption layer disposed on a first conductivity type group III-Vsemiconductor substrate; and a window layer disposed on the absorptionlayer, the window layer being composed of a compound semiconductorincluding P, having a band gap energy greater than a band gap energy ofthe absorption layer, and including a second conductivity type impuritybeing diffused in regions thereof corresponding to the plurality ofabsorption regions; wherein a surface defect density of the window layeris equal to or greater than 50 cm⁻² but not greater than 3000 cm⁻². 11.A photodiode array having a plurality of absorption regions arrangedone-dimensionally or two-dimensionally, the photodiode array comprising:an absorption layer disposed on a first conductivity type group III-Vsemiconductor substrate; and a window layer disposed on the absorptionlayer, the window layer being composed of a compound semiconductorincluding P, having a band gap energy greater than a band gap energy ofthe absorption layer, and including a second conductivity type impuritybeing diffused in regions thereof corresponding to the plurality ofabsorption regions; wherein an average area of surface defects of thewindow layer is equal to or greater than 3 μm² but not greater than 800μm².
 12. The photodiode array according to claim 9, wherein each of thesurface defects of the window layer has a concave or convex shape havinga height of 10 nm or more.
 13. The photodiode array according to claim9, wherein the window layer is composed of InP.
 14. The photodiode arrayaccording to claim 9, wherein the absorption layer has a multiplequantum well structure.
 15. The photodiode array according to claim 14,wherein the group III-V semiconductor substrate is an InP substrate, andthe absorption layer has a multiple quantum well structure in whichbarrier layers including InGaAs and well layers including GaAsSb arealternately laminated.
 16. The photodiode array according to claim 15,wherein the multiple quantum well structure of the absorption layer iscomposed of pairs of In_(x)Ga_(1-x)As (0.38≦x≦0.68) and GaAs_(1-y)Sb_(y)(0.36≦y≦0.62), or pairs of Ga_(1-u)In^(u)N_(v)As_(1-v) (0.4≦u≦0.8,0<v≦0.2) and GaAs_(1-y)Sb_(y) (0.36≦y≦0.62).
 17. A method formanufacturing an epitaxial wafer which is used for manufacturing aphotodiode array having a plurality of absorption regions arrangedone-dimensionally or two-dimensionally, the method comprising: anabsorption layer formation step of growing an absorption layer on afirst conductivity type group III-V semiconductor substrate; and awindow layer formation step of growing a window layer on the absorptionlayer, the window layer being composed of a compound semiconductorincluding P, and having a band gap energy greater than a band gap energyof the absorption layer; wherein in the window layer formation step, thewindow layer is grown by metal-organic vapor phase epitaxy using onlymetal-organic sources, and a growth temperature of the window layer isequal to or lower than a growth temperature of the absorption layer. 18.The method according to claim 17, wherein in the absorption layerformation step, the absorption layer is grown by metal-organic vaporphase epitaxy using only metal-organic sources.
 19. The method accordingto claim 17, wherein in the absorption layer formation step, theabsorption layer is grown by molecular beam epitaxy.
 20. The methodaccording to claim 17, wherein the growth temperature of the windowlayer is equal to or higher than 400° C. but lower than 600° C.
 21. Anepitaxial wafer used for manufacturing a photodiode array having aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, the epitaxial wafer comprising: an absorption layerdisposed on a first conductivity type group III-V semiconductorsubstrate; and a window layer disposed on the absorption layer, thewindow layer being composed of a compound semiconductor including P, andhaving a band gap energy greater than a band gap energy of theabsorption layer; wherein a surface defect density of the window layeris equal to or greater than 50 cm⁻² but not greater than 3000 cm⁻². 22.An epitaxial wafer used for manufacturing a photodiode array having aplurality of absorption regions arranged one-dimensionally ortwo-dimensionally, the epitaxial wafer comprising: an absorption layerdisposed on a first conductivity type group III-V semiconductorsubstrate; and a window layer disposed on the absorption layer, thewindow layer being composed of a compound semiconductor including P, andhaving a band gap energy greater than a band gap energy of theabsorption layer; wherein an average area of surface defects of thewindow layer is equal to or greater than 3 μm² but not greater than 800μm².
 23. The epitaxial wafer according to claim 21, wherein each of thesurface defects of the window layer has a concave or convex shape havinga height of 10 nm or more.